According to prior art, barrel-shaped cutting inserts may be formed by means of a process which includes that barrel-shaped green bodies are formed in a compaction device that comprises a die that is divided in an upper die part and a lower die part. The die parts are surrounded by an outer die part or a press table having a generally flat upper surface. When joined together, the upper die part and the lower die part define a chamber which defines the outer peripheral surface of the green body to be formed. Normally, the lower die part comprises a pressing bore extending from the lower surface thereof to said chamber, and the upper die part comprises a pressing bore that extends from an upper surface thereof to said chamber. There is also provided an upper punch arranged to slide through the upper pressing bore, and a lower punch arranged to slide through the lower pressing bore. During compaction, the respective punches are forwarded through the respective pressing bores such that the ends thereof reach said chamber and contribute to the definition of the outer peripheral surface of the green body by defining the opposite upper and lower surfaces thereof.
Prior to the compaction step, the upper die part is retracted or held in a retracted position in relation to the lower die part. The lower punch is retracted or held in a retracted position in the pressing bore provided in the lower die part. An upper surface of the lower die part is exposed as a consequence of the retraction of the upper die part. The exposed upper surface of the lower die part is in alignment with the upper surface of the surrounding press table, thereby enabling a powder filling device to be forwarded on said upper surfaces of the press table and the lower die part to a position in which it is enabled to introduce a powder into the part of the chamber defined by the lower die part, which defines an opening in said upper surface. Since the lower punch is retracted, powder is also introduced in the part of the pressing bore of the lower die part that is not occupied by the lower punch. After completion of the powder filling step, the powder filling device is retracted and the upper die part is forwarded to and joined with the lower die part. The compaction step is then performed by forwarding the lower and upper punch respectively to a position in which they, together with the inner walls of the respective die parts, define the shape of the green body to be formed. Finally, the upper die part is once again retracted, together with the upper punch, and the lower punch is further forwarded upwards in the direction of the pressing axis until the green body is fully exposed. Preferably the lower punch is forwarded until the upper surface thereof is in alignment with the upper surface of the lower die part. Thereby, a green body removal device, e.g. a robot arm, is enabled to remove the green body, and the main steps of the compaction sequence are finished.
The upper surface of the lower die part is flat, thereby enabling alignment with the upper surface of the press table and enabling the powder filling device to slide thereon and to fit tightly on top of and around the opening in said upper surface of the lower die part. Thereby, the risk of having powder escaping to the upper surface of the lower die part is efficiently suppressed. Powder remaining on the upper surface of the lower die will have a negative impact on the sealing between the upper and lower die parts and should therefore be avoided.
However, the above design is primarily suitable for the compaction of a barrel-shaped green body that has a parting line that is perpendicular to the pressing axis of the punches, and/or extends in one plane only. An upper inner edge of the lower die part extends along a line defining the parting line of the green body, and so does a lower inner edge of the upper die part. Should the parting line have a different than planar extension, the upper surface of the lower die part will have a contour corresponding to the contour of the parting line and will not be flat. This fact will make sliding of the powder filling device difficult due the fact that part of the lower die part will project from the plane defined by the upper surface of the outer die part or press table. If the contour is such that parts of the upper surface around said opening is below the level of the rest of said upper surface, it will be difficult to prevent powder from being gathered at those parts of the upper surface during powder filling. Such powder will have a negative impact on the sealing between the lower and the upper die parts.